The present disclosure relates to a non-linear Raman spectroscopy apparatus, and a non-linear Raman spectroscopy system and non-linear Raman spectroscopy method that use this apparatus. In more detail, the present disclosure relates to an apparatus, system, and method for multiplex coherent anti-Stokes Raman spectroscopy using a broadband light source as a Stokes beam.
Laser Raman spectroscopy is an analysis method of radiating a test sample with laser light having a single wavelength as a pump beam and obtaining spectrums of light scattered from the test sample. A shift amount of the wave number of a Stokes beam or an anti-Stokes beam, which is the scattered light mentioned above, with respect to the wave number of a pump beam is observed as a substance-specific spectrum, which corresponds to a molecular vibration mode unique to the substance of the test sample. Therefore, together with infrared spectroscopy, Raman spectroscopy has been widely used as spectroscopy for a molecular fingerprint region to analyze and evaluate substances, perform medical diagnoses, and develop organics such as new drugs and foods.
Non-linear Raman spectroscopy is similar to the laser Raman spectroscopy in the past described above in that Raman scattering light is measured, but is different therefrom in that a third-order non-linear optical process is used. The third-order non-linear optical process is to detect scattering light in three types of incident light as excitation beams, that is, a pump beam, a probe beam, and a Stokes beam. Examples include CARS (coherent anti-Stokes Raman scattering), CSRS (coherent Stokes Raman scattering), stimulated Raman loss spectroscopy, and stimulated Raman gain spectroscopy.
In CARS spectroscopy, in general, a test sample is radiated with a pump beam and a Stokes beam having a wavelength longer than that of the pump beam, and spectrums are obtained from non-linear Raman scattering light having a wavelength shorter than that of the pump beam scattered from the test sample (for example, refer to Japanese Unexamined Patent Application Publication No. 5-288681, Japanese Unexamined Patent Application Publication No. 2006-276667, and Japanese Unexamined Patent Application Publication No. 2010-2256). Also, a non-linear Raman spectroscopy method using white light as a light source for generating a Stokes beam has been suggested in the past (refer to Japanese Unexamined Patent Application Publication No. 2004-61411 (Japanese Patent No. 3691813)).
On the other hand, in CARS spectroscopy in the past described above, ultrashort pulse light of several tens of fs to several tens of ps is used as laser light for generating a pump beam and a Stokes beam. In this case, there is a problem such that an apparatus for use in CARS is expensive and complex. To avoid this problem, a method of using a supercontinuum light excited by a short pulse having a pulse width of 0.1 ns to 10 ns with a photonic crystal fiber (PCF) has been suggested (refer to Japanese Unexamined Patent Application Publication No. 2009-222531).
Compared with Raman spectroscopy in the past, non-linear Raman spectroscopy typified by CARS spectroscopy described above can avoid an influence of fluorescence background, and further improve detection sensitivity. For this reason, non-linear Raman spectroscopy has been actively studied and developed particularly as a molecular imaging technology of biosystems.